Posts are stored in the _posts directory and named according to the YEAR-MONTH-DAY-title.MARKUP format as per the usual.

Where YEAR is a four-digit number, MONTH and DAY are both two-digit numbers, and MARKUP is the file extension representing the format used in the file. For example, the following are examples of valid post filenames:

2016-07-20-writing-jekyll-posts.md
2015-01-03-static-site-generators.markdown

Recommended Front Matter Defaults:

defaults:
  # _posts
  -
    scope:
      path: ""
      type: "posts"
    values:
      layout: "post"

ProTip: Remember to write unique excerpt descriptions for each post for improved SEO and archive listings.